0. T. Sherman — A Study of Thermometers. 



43 



a degree in the first twelve hours, but no change was detected 

 in the following hundred and eight. 



The question presents itself, What is the state of the ther- 

 mometer after such treatment? First, as regards the action of 

 the zero. In the adjoining cut we have compared the motion 

 of the zeros of four thermometers before and after treatment. 



100° 

 Before heating 



200° 300° 0° 



(Centigrade.) 



After heating. 



Movement of the Zero. 



In the first series the influence of the rise is evident. The 

 second series is free therefrom. The movement of the zero 

 for the higher temperatures is similar to that for lower; or 

 the mere fact of heating the thermometer now produces no dis- 

 tortion from which the instrument will not sensibly recover. 



Does the instrument after treatment repeat its readings when 

 exposed to similar conditions? Do its indications vary with 



